1. Field of the Invention
Transesterifications are equilibrium reactions and are subject to acid or base catalysis. Ether linkages can also be susceptible to both acid and base cleavage and, in such cases, for each ether linkage cleaved, two new impurities can be formed when attempting transesterifications of ether containing substrates.
2. Description of Prior Art
Substituted-2-pyridyloxyphenoxy alkane carboxylic acids and their derivatives are known compounds having utility as herbicides. Such products are described in, for example, European Pat. No. 483 and British Pat. No. 1,599,121.
The various derivatives of such acids do not necessarily have the same efficacy or effectiveness against different plant species and, accordingly, it is sometimes desirable to modify the molecule to obtain the desired results. However, when transesterifications of, for example, 2-(4-((3-chloro-5-(trifluoromethyl)-2-pyridyl)oxy)phenoxy)propanoic acid esters, such as transesterifying the methyl ester to the butyl ester, are carried out to high conversions with conventional acid and base transesterification catalysts, e.g., toluene sulfonic acid, ion exchange resins, sodium methoxide, sodium carbonate and potassium carbonate, from 0.5 to 2.2 percent or more pyridyl ether cleavage is obtained. With higher boiling alcohols, the ether cleavage becomes a more severe problem, with the combined impurities produced by ether cleavage approaching 10 percent.